Lap welding method, lap joint, production method of lap joint, and an automobile part
AssigneeNippon Steel Corporation
InventorsHiroki Fujimoto, Tohru Okada, Takashi Imamura
Life of this patent
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Abstract
The present invention has as its object to inhibit fracture due to a HAZ softened part in substantially circular laser lap welding taking the place of resistance spot welding for joining a superposed plurality of steel sheets including a high strength steel sheet. To solve this problem, the inventors discovered lap welding comprising superposing a plurality of steel sheets and firing a laser to form a substantially circular laser weld (1), which lap welding firing the laser in a straight line through an outer edge of the substantially circular laser weld (1) so as to form a hardened part (8) at the steel sheets and thereby suppressing fracture arising from the HAZ softened part.
Claims14
Lap welding method comprising superposing a plurality of steel sheets and firing a laser to form a substantially circular laser weld, which lap welding method comprises scanning the laser in a straight line through an outer edge of said substantially circular laser weld so as to form a hardened part at the steel sheets,
- wherein the hardened part is a reheated and hardened HAZ-softened part formed by the substantially circular laser weld,
- wherein a laser scanning width is at least 10% and 50% or less of a diameter of the substantially circular laser weld,
- wherein said straight line laser scanning operation scans the laser over at least 3 mm from the outer edge of said substantially circular laser weld, and
- wherein at least one steel sheet among said plurality of steel sheets is a steel sheet having a martensite structure.
A lap joint obtained by superposing a plurality of steel sheets and firing a laser to form substantially circular laser weld so as to join said plurality of steel sheets, which lap joint is provided with a hardened part formed in a straight line by firing the laser through an outer edge of said substantially circular laser weld,
- wherein the hardened part is a reheated and hardened HAZ-softened part formed by the substantially circular laser weld,
- wherein a laser scanning width is at least 10% and 50% or less of a diameter of the substantially circular laser weld,
- wherein said straight line laser scanning operation scans the laser over at least 3 mm from the outer edge of said substantially circular laser weld, and
- wherein at least one steel sheet among said plurality of steel sheets is a steel sheet having a martensite structure.
A method of production of a lap joint produced by superposing a plurality of steel sheets and firing a laser to form a substantially circular laser weld, which method of production of a lap joint comprises scanning the laser in a straight line through the outer edge of said substantially circular laser weld so as to form a hardened part at the steel sheets,
- wherein the hardened part is a reheated and hardened HAZ-softened part formed by the substantially circular laser weld,
- wherein a laser scanning width is at least 10% and 50% or less of a diameter of the substantially circular laser weld,
- wherein said straight line laser firing operation fires the laser over at least 3 mm from the outer edge of said substantially circular laser weld, and
- wherein at least one steel sheet among said plurality of steel sheets is a steel sheet having a martensite structure.
Dependencies are inferred from the claim text.